The present invention relates to a transparent digitizer and, more particularly, but not exclusively to a transparent digitizer with a cordless stylus or like input device.
U.S. patent application Ser. No. 09/628,334 “Physical Object Location Apparatus and Method and a Platform using the same” to Gamalong Ltd, the contents of which are hereby incorporated by reference, describes an electromagnetic method for locating physical objects on a flat screen display, that is to say a digitizer that can be incorporated into the active display screen of an electronic device. The present disclosure concerns further technical methods for implementing a transparent sensor based digitizer.
Touch technologies are commonly used as input devices for a variety of products. The usage of touch devices of various kinds is growing sharply due to the emergence of new mobile devices, such as Web-Pads, Web Tablets, PDAs, Tablet PCs and wireless Flat Screen Displays. These new devices are usually not connected to standard keyboards, mice or like input devices, which are deemed to limit their mobility. Instead there is a tendency to use touch input technologies of one kind or another.
Some of the new mobile devices, such as the Tablet PC, are powerful computer tools. Devices such as the Tablet PC use a stylus based input device, and use of the Tablet PC as a computing tool is dependent on the abilities of the stylus input device. The input devices have the accuracy to support hand writing recognition and full mouse emulation, for example hovering, right click, etc. Manufacturers and designers of these new mobile devices have determined that the stylus input system can be based on various electromagnetic technologies, which can satisfy the very high performance requirements of the computer tools in terms of resolution, fast update rate, and mouse functionality. However, in general, the stylus systems in use are tablet based, that is the stylus is moved over a tablet which in itself is not a screen. There have been attempts in the past to combine non-transparent electro magnetic digitizer technology with a transparent Flat Screen Display. U.S. Pat. No. 6,005,555 to Wacom describes a digitizer comprising two layers of orthogonal conductive loops. One set of conductive loops is used for transmitting an excitation signal while the orthogonal set of loops is used for receiving oscillations. However, a requirement of the Wacom system is high conductivity within the loops. As such, Wacom's method has to use loops made of standard metallic conductors and cannot be used with transparent conductive foils, since the resistance of a conductive transparent line is very high. Using high resistance conductive loops to energize the stylus requires a particularly high voltage input, in excess of 1 KV, which makes this solution impractical. Without the use of transparent conductive material, however, the solution of Wacom merely succeeds in making the display difficult to view.
One way of overcoming the difficulty of viewing the display is to place the non-transparent sensor of Wacom behind the display. Thus the sensor may be located between the FPD back-light and the electronic board of the display device. As such, integration of a non-transparent sensor into a FPD device is a very complicated and expensive process. Such mounting typically requires shielding of noisy components within the device and sometimes requires the manufacturing of a special slot in the FPD structure, in which the sensor is mounted.
A non-transparent sensor, if located behind the display, is inevitably relatively far away from the tip of the stylus whose position it is trying to determine. Due to the relatively long distance from the sensor, non-transparent sensors suffer from parallax, leading to inaccurate positioning of the stylus. Positioning is especially inaccurate, that is parallax effects are especially large, when the stylus is held at an angle to the display. Yet, applications such as handwriting detection demand that the system is tolerant to the stylus being held at an angle to the screen.
Furthermore, again due to the relatively long distance from the sensor, back-mounted sensors suffer from inaccurate positioning of the stylus when the stylus is held close to the edge of the sensor.
In summary, due to the relatively long distance from the sensor, and furthermore due to the number of electronically active components likely to be located between the sensor and the stylus, back-mounted sensors may not achieve reliable positioning resolution.
There have been attempts in the past to overcome the disadvantages of a back mounted sensor by implementation of a sensor based on a transparent foil. As the sensor is transparent it can be mounted on the front of the screen. However, such a detector relies on transparent conductors, which have a high resistivity compared to opaque conductors. U.S. Pat. No. 5,381,160 to Kurta describes a foil comprising two transparent layers of orthogonal conductors. Kurta's disclosure describes a solution to a problem that arises in light of the above-mentioned high resistivity of the conductors, namely how to excite the physical object whose position is to be determined despite the high resistivity. The solution is simply to use an active stylus, internally powered by its own battery. The stylus therefore does not require external excitation. However, an active, battery powered stylus is generally not regarded as a satisfactory solution for a number of reasons. For example, an active stylus requires continuous maintenance and may even stop working and thereby render the entire computer device inoperable. Also the active stylus requires recharging, and is more expensive than a passive device. Therefore, an active stylus is currently unacceptable for the mobile consumer market.
The above-mentioned application to Gamalong discloses a sensor, for a passive stylus, based on transparent foils where a separate excitation coil is located about the screen. The stylus or other object whose position is to be detected comprises a resonant circuit. The resonant circuit is excited by the excitation coil to generate an electric field, and the electric field is detected by the relatively highly resistive detection conductors on the transparent foils. A problem however, is that detection, which is based on electric fields, is carried out on the surface of an electronic display screen, and the screen surface is a relatively high noise environment in terms of electromagnetic activity. The high noise environment necessarily reduces the resolution level of the digitizer.
There is thus a widely recognized need for, and it would be highly advantageous to have, a stylus based transparent digitizer devoid of the above limitations.